A monocrystal ofFe 3 O 4 is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT v=123.76 K with activation energy E=92.5 meV at T >T v and temperature-substitute for the activation energy below the VT,T 0=E/k B≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change in the magnetic moment ΔM≈0.21 ΔM≈0.21μ B and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT v. The magnetic characterization established self consistentlyT v as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ B and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization of the monocrystal (88%) with additional natural and imposed defects contributing as 12%.
Fe(2 ML)/V(y ML) and interleaved Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) superlattice systems with spacer thicknesses, y, (4 ≤ y ≤ 17) were investigated macro-magnetically to estimate the coupling strength and the magnetoresistance in these materials, and particularly in the antiferromagnetically coupled monolayers. The results from the magnetic and magnetoresistive measurements indicate that adding one monolayer of Fe increases the antiferromagnetic coupling and the magnetoresistivity ratio from 0.0075 mJ/m2 at 20 K and 2 % at 10 K for Fe(2 ML)/V(y ML), to 0.05 mJ/m2 and 2.5 % for Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) at the same temperatures. Both systems exhibit in-plane magnetic and magnetoresistive isotropy, therefore the increase of the conferred physical parameters is attributed mainly to the stresses at the interface as governing mechanisms over the magnetoelastic forces.
The organization of magnetic materials into one-dimensional micro- and nanowires on designed media is discussed, exemplified by two experiments on the microscale and nanoscale, with regard to particles as basic building blocks for the growth and development of matter. In the first organizational experiments, cobalt (Co) micro-particles are assembled on patterned media with perpendicular magnetization by acoustic vibrations onto designed shapes reflecting macroscopically the parent material. In the second experiments, semiconductor Germanium-Dysprosium (Ge98Dy2) matter is assembled on gold (Au) catalytic nuclei in a tube reactor by physical vapor transport as clusters of nanowires. The underlying mechanisms of organization are described, and similarities and distinctive features in the processes are discussed. The role of the energy-input in the form of mechanical vibrations and heat is outlined with its similar impact on the assembly and growth of matter on surfaces. The description of these experiments in view of organization allows more control over the processes of planned arrangement on designed media. Routes for further progress in this direction are briefly outlined.
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